# std::exp(std::valarray)

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< cpp‎ | numeric‎ | valarray

Defined in header `<valarray>` |  |
template< class T > valarray<T> exp( const valarray<T>& va ); |  |

For each element in va computes e raised to the power equal to the value of the element.

### Parameters

va | - | value array to apply the operation to

### Return value

Value array containing e raised by the values in va.

### Notes

Unqualified function (exp) is used to perform the computation. If such function is not available, std::exp is used due to argument-dependent lookup.

The function can be implemented with the return type different from std::valarray. In this case, the replacement type has the following properties:

  - All const member functions of std::valarray are provided.
  - std::valarray, std::slice_array, std::gslice_array, std::mask_array and std::indirect_array can be constructed from the replacement type.
  - For every function taking a const std::valarray<T>& except `begin()` and `end()`(since C++11), identical functions taking the replacement types shall be added;
  - For every function taking two const std::valarray<T>& arguments, identical functions taking every combination of const std::valarray<T>& and replacement types shall be added.
  - The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

### Possible implementation

    template<class T>
    valarray<T> exp(const valarray<T>& va)
    {
        valarray<T> other = va;
        for (T& i : other)
            i = exp(i);

        return other; // proxy object may be returned
    }

### Example

This example demonstrates the Euler's identity eiπ
= -1 and the related exponents.

Run this code

    #include <complex>
    #include <iostream>
    #include <numbers>
    #include <valarray>

    int main()
    {
        const double pi = std::numbers::pi;
        std::valarray<std::complex<double>> v =
        {
            {0, 0}, {0, pi / 2}, {0, pi}, {0, 3 * pi / 2}, {0, 2 * pi}
        };
        std::valarray<std::complex<double>> v2 = std::exp(v);
        for (std::cout << std::showpos << std::fixed; auto n : v2)
            std::cout << n << '\n';
    }

Output:

    (+1.000000,+0.000000)
    (+0.000000,+1.000000)
    (-1.000000,+0.000000)
    (-0.000000,-1.000000)
    (+1.000000,-0.000000)

### See also

log(std::valarray) | applies the function std::log to each element of valarray (function template)
expexpfexpl (C++11)(C++11) | returns e raised to the given power (\({\small e^x}\)ex) (function)
exp(std::complex) | complex base e exponential (function template)

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